The present invention relates to encapsulated electrostatographic toners and, more particularly, to an electrostatographic toner material which comprises a pressure fixable core encapsulated in a pressure rupturable shell with the outer surface of the shell being hydrophobic. Preferably, the outer surface of the shell is rendered hydrophobic by precipitating at least one thermosetting resin onto the pressure rupturable shell. The present invention also relates to a process for preparing an encapsulated electrostatographic toner material.
Electrostatography involves developing a tone electrostatic latent image contained on a photoconductive or dielectric surface with a toner material containing a colorant and a binder to produce a visible toner image, and then transferring and fixing the visible toner image onto a surface such as a paper sheet. The development of the latent image utilizes either a combination of a toner material with carrier particles or a toner material only. The process for fixing the toner image to the paper sheet can be accomplished by heat fixing, solvent fixing or pressure fixing.
Encapsulated electrostatographic toner materials for use in pressure fixing are well-known, as disclosed by, for instance, U.S. Pat. No. 4,307,169 which discloses production of such toners by interfacial polymerization. In this prior art process, it has been necessary to spray dry the resulting slurry of particles to produce a free-flowing, dry powder. Obtaining a toner material in the form of a free-flowing, dry powder is desirable to permit easy handling of the toner.
However, the spray drying process suffers from the disadvantages that it can require costly spray drying equipment, can consume a large quantity of energy and can also restrict the potential use of heat sensitive or volatile components in the core material of the toner. Therefore, there has been a need for a process of producing encapsulated toner materials in the form of a dry, free-flowing powder that does not require spray drying.
Various attempts have been made to produce dry, free-flowing encapsulated toner particles by interfacial polymerization without spray drying. The inventor has attempted to obtain toner particles in the form of a dry powder by filtering, by air drying and by oven drying the slurry of capsules; however, such attempts have been unsuccessful due to the tendency for the capsules to cake and agglomerate. Up to now, spray drying has been necessary to keep the particles separated during the drying process.
It is therefore an object of the present invention to provide an improved encapsulated toner material that overcomes the disadvantages of the prior art.
It is another object of the present invention to produce electrostatographic toner particles by interfacial polymerization that are in the form of a dry, free-flowing powder.
It is another object of the present invention to produce encapsulated electrostatographic toner particles by interfacial polymerization without the necessity of spray drying the particles produced.
It is another object of the present invention to minimize the caking or agglomerating of capsules during the process for producing an encapsulated electrostatographic toner material.
It is another object of the present invention to provide an energy efficient process for producing dry, free-flowing electrostatographic toner particles by interfacial polymerization.
It is a further object of the present invention to provide encapsulated electrostatographic toner materials capable of containing volatile or heat sensitive core materials.